The present invention relates to a discrete (or discontinuous) event model computer simulation method and an apparatus for estimating the optimum production conditions at the scene of production, and more particularly to such a simulation method and apparatus suitable in the case where the modification of a simulation model is made in a trial and error manner.
JP-A- No. 62-135958 has disclosed a simulation system in which a process of simulation is stored and the results of simulation are produced as outputs on the basis of the stored contents. JP-A- No. 61-237162 has disclosed a simulation system in which a simulation model is. partially modified and simulation is thereafter performed again. More especially, all possible events which may occur are preliminarily determined in performing the first simulation. Thereafter, when the simulation model is modified, calculation is again made for only events which have any change induced by the model modification.
However, in the case of the simulation process storing system disclosed by the JP-A- No. 62-135958, the simulation process is merely stored or the stored contents are not utilized for a "processing for returning" of the simulation process. The term of "processing for returning" means that the simulation process is turned back to the previous or older instant (or point) of time and the simulation process is again performed starting from the returned point of time. In the simulation system of the JP-A- No. 62-135958, resimulation will be made in such a manner that the simulation process is returned to a start point thereof and simulation is again performed starting from the start point. In the simulation system disclosed by the JP-A- No. 61-237162 in which the results of a (first) simulation process before model modification are used for a (second) simulation process after model modification, the simulation process after model modification requires a longer calculation time as compared with the simulation process before model modification in the case where the influence of model modification extends over a wide area. In the case where it is estimated or presumed that the simulation process after model modification needs a calculation time longer than the simulation process before model modification, the simulation process after model modification is stopped but must be continued in a simulation manner performed before model modification.
In addition to the above-mentioned inconveniences, the following problem exists in the case where the production conditions at the scene of production are simulated. Namely, in the scene of production, the capacity of a certain production or manufacturing equipment may not be changed at just any point of time in the course of simulation but must be changed at a specified point of time (for example, early morning of Friday) during a simulation period (for example, from Monday to Friday). In such a case, it is required that the simulation process is returned from the course of the simulation process (for example, about 10 a.m. of Friday) to the specified point of time. However, in the conventional method, the simulation process is again performed or retraced from a start point thereof and hence a lot of time is consumed for unnecessary simulation process.